The present invention concerns a method and a kit for early pregnancy detection.
Pregnant women secrete soon after the implantation of a fertilized ovum in the chorionic tissues an increasing amount of human chorionic gonadotropin (HCG) some of which is excreted in the urine. Most presently available pregnancy detection methods are based on the detection of HCG in the urine.
One group of known methods for the detection of HCG in the urine is based on radioimmunoassay. While these methods are very reliable and sensitive they require highly sophisticated laboratory equipment and such tests cannot be carried out by the subjects themselves.
Another group of tests known as enzyme linked immunosorbents assay (ELISA) is based on an enzymatic reaction associated with HCG as described, for example, in Israel patent specification No. 48741 (Rafa Laboratories). In accordance with that method a solution of an anti-HCG antibody labelled with an enzyme is mixed with a urine sample to be tested. The mixture obtained is then mixed with anti-HCG antibody associated with a carrier. In the absence of HCG in the urine, subsequent washings and centrifugations of the substrate will remove the anti-HCG antibody with the enzyme linked thereto. Accordingly, addition to the residue remaining in the vessel of a non-coloured solution capable of developing a colour in the presence of the enzyme will in this case not give rise to the development of any colour. If, however, HCG is present the enzyme will be retained in the residue. In that case the addition of the said solution will give rise to the development of a colour.
This and similar methods have however not been commercialised, apparently for the reason that they are not sufficiently sensitive and reliable.
Another group of known methods is based on agglutination that occurs upon reaction of anti-HCG antibodies adsorbed on a carrier such as latex particles, and HCG present in the test fluid, or the prevention of agglutination of HCG sensitized latex particles or red cells. In the direct, agglutination method anti-HCG antibody bearing material is contacted with the tested urine and if the latter contains HCG there occurs an agglutination which can be detected visually. In accordance with the indirect, agglutination inhibition method anti-HCG antibodies are contacted with the tested urine and subsequently with a reagent comprising HCG deposited on gel particles or on red blood cells. If the urine contains HCG the latter reacts with the anti-HCG antibodies with the consequence that the subsequently added HCG reagent does not cause agglutination. If, however, the tested urine does not contain any HCG the anti-HCG and HCG reagent react with each other with consequential agglutination.
Such methods are described, for example, in European patent application No. 0014965 (Hoffmann-La Roche), U.K. patent No. 1,561,920 (Warner Laboratories), Israel patent No. 50929 (American Home Products Corporation) and Israel patent No. 47223 (Rafa Laboratories).
Some of these methods have become commercial and are even used for do-it-yourself testing. However, these methods have some drawbacks in that they are of limited sensitivity, not sufficiently reliable in that they produce a relatively high proportion of false positive and false negative results, and cannot be employed in the very early stages of pregnancy.
The early and reliable detection of pregnancy is of great importance. Thus, where for some reason the pregnancy is undesired and has to be interrupted it is important to establish the pregnancy in as early a stage as possible. In other cases, where the woman is in the habit of taking certain drugs which may be teratogenic, it is important to know of the pregnancy as early as possible so that the taking of such drugs may be interrupted. In still other cases where it is known that the woman will suffer from certain ailments in consequence of pregnancy, e.g. an inability to hold the fetus under normal conditions, adequate treatment has to be initiated as soon as possible.
As a rule women are reluctant to go to laboratories for testing at an early stage of a missed period, be it because of the trouble that this involves or be it for psychological reasons.